Research On The Concentration Of Nutrients In Decentralized Wastewater By SFCW-FA

Seriously polluted water environment discounted welfares of people with extremely small per capita water resource in china.Given great achievements have been made on the treatment of industrial and municipal domestic wastewater?MDW?,Chances of further reduction in the discharge of effluent contaminants are very sleem.Rural wastewater can be classified as decentralized wastewater?DW?which is poorly treated over the nation,and become the principal source for surface water pollution due to underdeveloped treatment technology.The statistics of frequency of water quality indicators?WQI?for surface waters allover the nation had been studied.Results indicate that nutrients such as nitrogenous and phosphorus salts ranked top among the contaminants,and play key roles in the concentration of nutrients from DW to improve surface water quality.Compare to MDW,DW is characterized by higher ratio of BOD/COD,lower biological toxicity.Considered the far open extent and shorter flow path of collection system of DW than that of MDW,reinforcements of pretreatment,organic removal,nutrient removal and reclamation need to be adapted to the treatment techniques of DW.Physical and chemical methods are not suitable for the enrichment of low-strength nutrients contained in the effluent from bio-ecological treatments of DW which can usually meet the highest criterion in GB18918-2002.It's appropriate for rural cultural wetlands to be applied to contrite and reclaim nutrients within the effluent from bio-ecological treatment of DW without risks of ecotoxicity.Surface-flow constructed wetlands dominated by filamentous algae?SFCW-FA?are researched to concentrate the nutrients in DW in this paper.FA are characterized by huge biomass,assimilative capacity of nutrients and prone to be separated from water.Effectively driven by solar irradiation?SIR?,SFCW-FA is assumed to deprive nutrients from passing DW and provide suitable habitat and adequate food for a complex community of animal-feeding microbes?AFM?.Firstly,references on Chinese fresh algae were studied to find out FAs that are appropriate to grow in Taihu lake watershed.Wild algae were collected to colonize SFCW with mixed FA?SFCW-MFA?,from which FA inocula were seperated through isolation methods of algae filament?AFI?,vegetative cell?VCI?and apical cell?ACI?.These FA inocula were tested to consume nutrients at different temperatures and identified so as to be quickly acclimated to native waters.Secondly,inocula of fragment FA?FI-FA?,FA spores?SI-FA?,immobilized FA spores?ISI-FA?and autogenetic FA?AG-FA?were cultured to breed FA in SFCW.Mechanisms of multidimensional ecological niches are concluded to explain the establishing process of dominant FA populations in SFCW-FA.Thirdly,SFCWs dominated respectively by Cladophora?FA mixture of Cladophora,Pithophora and Basicladia,SFCW-CLA?,Rhizoclonium?SFCW-RHI?,Oedogonium?SFCW-OED?,Spirogyra?SFCW-SPI?,Tribonema?SFCW-TRI?and autogenetic Cladophora?SFCW-ACLA?were established.Experiments were carried out in these SFCW-FAs to concentrate effluent nutrients from a bio-ecological treatment facility on domestic wastewater from a small campus.Polynomial fitting,multivariate linear regression and stepwise regression were applied on data obtained from the concentrating kinetic tests.Finally,wild Carassius auratus?C.auratus?were added as aquatic macroconsumer of SFCW-ACLA to perform top-down bio-manipulation experiments.Afore-mentioned experimental results are as following:Based on overall consideration of alga morphology,concentrating efficiency,environmental tolerance and potential ecological risks,80 FA were selected out and classified into twenty-one genera,ten families,eight orders,and three classes of two alga phyla.Twelve FA were isolated from the SFCW-MFA and classified into eight genera?Ulothrix,Oedogonium,Cladophora,Rhizoclonium,Basicladia,Pithophora,Spirogyra and Tribonema?.FA purities?FAP?of the isolation methods?AFI,VCI,ACI?increase on the sequence,inversely correlate with the width of FA(R_0.007=-0.852?R_0.008=-0.849?R_0.047=-0.713)and the length of FA inocula.Logarithms of mass yields?LMY?of the three isolation methods correlate with the length of FA inocula,while LMYs of VCI and ACI significantly correlate with the width(R_0.019=0.792,R_0.001=0.920).Results of stability tests of algal filaments show that Ulothrix is the most instable whereas Rhizoclonium is the most stable and resistant for year-round changes in temperature.Vegetative reproduction of FA correlate with nutrient consuming rates?NCR,[TN,TP,TIC]?as R_0.017=0.803,R_0.099=0.624and R_0.019=0.792.Pithophora filament reproduces vegetative cells at the fastest rate of 53.6±24.9(?m h^-1),and consumes TN,TP and TIC at fastest rates of 10.46?0.57 and 19.66(mg g^–1 d^–1)respectively.Temperatures for five succession states of FA isolated from SFCW-MFA compose the year-round succession table.Ulothrix and Hydrodictyon are prohibited from colonizing the SFCW-FA since they are instable and hazard for aquatic ecosystem.In breeding stage,the FA succeeded in colonizing the SFCW-FA respectively.Cladophora dominated the SFCW-CLA with highest relative dominant frequency?RDF?of 94.4%±4.0%,whereas Rhizoclonium scored the lowest RDF of 73.5%±6.8%in SFCW-RHI.Evidences from these SFCW-FA support that FA dominate the SFCW-FA by occupying top multidimensional ecological niches consist of SIR competition,temperature restriction,nutrients limitation,biological interaction,and growing style.Results from SFCW-ACLA indicate that growth rate?GR?of Cladophora is restricted by temperature and SIR rather than nutrient.Surface coverage?SC?represents the SIR and available nutrients,and is appropriate for the manipulation of SFCW-ACLA.The speculation of rendering SC adaptable to regulate GR at the end of linear zone to achieve the removal of nutriens from DW and harvest of FA along with the mingled AFM,is put forward and supported by the results from nutrients concentrating experiments?SC=95%⁹8%?on SFCW-CLA?SFCW-OED?SFCW-RHI and SFCW-SPI.By multivariate linear regression,data from SFCW-CLA,SFCW-OED,SFCW-RHI can be regressed into models of concentrating kinetics with judging coefficients higher than 0.914?SFCW-RHI?and significant F tests?F>F0.05?4,8?=3.838?.By stepwise regression,qualified kinetics models for other two SFCW-FAs are established with significant tests of F=41.6474>F_0.05?10,2?=19.396 for SFCW-TRI and F=4.556>F_0.05?6,6?=4.284 for SFCW-SPI.Maximal judging coefficient is obtained for SFCW-TRI?0.968?whereas the minimum for SFCW-SPI?0.695?.Results from feeding experiments show that C.auratus has preferences for different FA in ingestion ratio and weight-gain ratio.For Cladophora,Rhizoclonium,Spirogyra and the mixture FA?Oedogonia and Rhizoclonium?,the significance levels(p_t-test)in ingestion ratio and weight-gain ratio are 0.008,0.010,0.014,0.004,and 0.013,0.009,0.010,0.007.Feeding stresses influence the ratios of ingestion?P<0.031?and weight-gain?P<0.016?with significant levels,except insignificant level?p=0.092?between medium competitive feeding?MCF?and uncompetitive feeding?UCF?on weight-gain ratio.Feeding stresses increase the average ratios of ingestion and weight-gain.There are significant differences on C.auratus digestion of different FA,since complete microscopic morphology of Pithophora akinetes and Rhizoclonium filaments in the debris of end intestinal tract of C.auratus were observed.To a light extent?UCF and MCF?in the strength of bio-manipulation,no significant influence was detected in the quality of effluent from the SFCW-ACLA.However,the decrease in population density of Chironomid larva was more than 78.4%.High strength bio-manipulation improved effluent quality significantly in a short time,but in the end,led to the extinction of Cladophora and the shift of alga dominance from Cladophora to suspended unicellular Chlorophyta in separate or grouped forms,and the significant exceedance of TP criteria.To sum up,low strength of nutrients contained in DW can be effectively concentrated by SFCW-FA.Special kinetic models descript the assimilative behavior of FA accurately when they dominated the SFCW via multidimensional ecological niche.FA and AFM can be reclaimed by simple operation or bio-manipulation based on top-down effect.